Metabolic disorders such as type 2 diabetes, obesity, and all of the related complications, are leading causes of mortality. These disorders are associated with the excessive nutritional intake and lack of exercise of the Western lifestyle, and increasingly that of the rest of the world. Type 2 diabetes is a debilitating disease characterized by high-circulating blood glucose, insulin, and corticosteroid levels. The incidence of type 2 diabetes is high and rising and is becoming a leading cause of mortality, morbidity, and healthcare expenditure throughout the world (Amos et al., Diabetic Med. 14:S 1-85, 1997). Diabetes (and insulin resistant conditions) result in elevated levels of glucose in the blood. Prolonged high blood sugar may cause blood vessel and nerve damage.
Various pharmacological approaches for the treatment of type 2 diabetes are available (Scheen et al., Diabetes Care, 22(9):1568-1577, 1999). One such approach is the use of thiazolidinediones (TZDs), which represent a new class of oral antidiabetic drugs that improve metabolic control in patients with type 2 diabetes. TZDs (including rosiglitazone (Avandia®) and pioglitazone (Actos®)) command a large share of the current antidiabetic drug market. TZDs reduce insulin resistance in adipose, muscle, and liver tissues (Oakes et al., Metabolism 46:935-942, (1997); Young et al. Diabetes 44:1087-1092, (1995); Oakes et al., Diabetes 43:1203-1210, (1994); Smith et al., Diabetes Obes Metab 2:363-372 (2000)). TZDs also lower the levels of free fatty acid (FFA) and triglycerides.
TZDs administered alone or in combination with metformin have glucose-lowering effects in patients with type 2 diabetes and reduce plasma insulin concentrations (i.e., in hyperinsulinaemia) (Aronoff et al., Diabetes Care 2000; 23: 1605-1611; Lebovitz et al., J Clin Endocrinol Metab 2001; 86: 280-288; Phillips et al. Diabetes Care 2001; 24: 308-315). Abnormalities in lipid levels can also be treated (Day, Diabet Med 1999; 16: 179-192; Ogihara et al. Am J Hypertens 1995; 8: 316-320), high blood pressure (Ogihara et al. Am J Hypertens 1995; 8: 316-320) and impaired fibrinolysis (Gottschling-et al. Diabetologia 2000; 43:377-383). However, there are numerous side effects associated with the use of TZDs, such as weight gain, liver toxicity, cardiovascular toxicity, upper respiratory tract infection, headache, back pain, hyperglycemia, fatigue, sinusitis, diarrhea, hypoglycemia, mild to moderate edema, fluid retention, and anemia (Moller, Nature, 2001, 414: 821-827). Accordingly, there is a need for improved therapeutic approaches to metabolic disorders that have fewer adverse effects than the available pharmaceutical approaches utilizing TZDs.